There is a tinning compound that comes in paste form, we use it to line
contact areas on pressure vessels. I am not sure of its use for food
items though. A better choice would be pure tin bars and try applying
it directly but it may need some kind of flux to bond to the steel ??.
I found some in the McMaster carr site, 100% virgin tin for about
$17/lb. item #8886K11
I also found this site http://www.retinning.com/

Glenn Ashmore wrote:
You can send it off to a professional tinker or do it yourself.

The professional way is to use bar tin and flux over a hearth of crushed
firebrick but there is an easier way that works almost as well. You can get
most of the material from a stained glass supplier. Just make sure the
solder is pure tin.

I used Johnson's E-127 Flux N Solder pure tin to retin some copper pots. It
is a paste of flux and pure tin powder. Clean the pan well and make sure it
is free of grease. Sand off any rust. I used some fresh carburator cleaner
and then rensed off thoroughly. Coat anything that you don't want the tin
to get on with whiting chalk and set it aside to dry. Brush the paste on
thinly and evenly then heat the pan with a propane torch (preferably from
the outside) until the solder melts. About 450F. Don't over heat and keep
the torch moving to prevent hot spots.

A much better way to do it if you have a propane fish cooker is to set a
larger pan full of 1/4" chunks of crushed fire brick on the cooker and set
the pan to be retinned down into the bed of crushed brick. It will heat a
lot more evenly. Don't use fine stuff because if any gets into the tin it is
impossible to get it out.

Once the tin is all melted swish it around to make sure all the metal is
coated and pour out the excess. Quickly, while still molten, wipe the pan
with a thick piece of wool to level the tin.

Steel is a little harder to heat evenly than copper but a steel pie tin will
be easier to do than a copper pot because you don't have to worrry about
getting the tin on the outside copper.